I'll bite on some guesses, not sure which the OP is talking about. A) Historically, before computing was fast enough, digital synthesizers often had major issu

I'll bite on some guesses, not sure which the OP is talking about. A) Historically, before computing was fast enough, digital synthesizers often had major issues with aliasing (which could be defined as "lower quality", certainly it could be defined as unwanted artifacts. Although conversely some saw the aliasing as a sort of a "character"). IMHO this is no longer as big of a problem with the fast computing power today: techniques like oversampling, BLEP for oscillators, etc. exist to minimize aliasing. There is possibly a few mathematical issues out there for any "real time" oriented calculations due to the quantized nature of sampled audio, but software engineers even are coming up with techniques to deal with some of them (this paper -- https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_1.1.1.pdf https://www.native-instruments.com/fileadmin/ni_media/downlo... -- is well known for going over some solutions for filters for instance). B) The other possibility: the nice thing (or not so nice thing, depending on your point of view) about subtractive synthesis with pure waveforms, is you are usually starting out with waveforms that are harmonic in nature (like a square wave or sawtooth). With techniques like additive (Razor's technique), digital FM / PM, or the like, it's much easier to get non-harmonic sounds. I wouldn't call this "lower quality", just different.